Conventionally, e.g., air conditioners each including a heat pump device have been known as air conditioners mounted on hybrid vehicles, electric vehicles, etc. These heat pump devices for vehicles are each configured such that an electric compressor, an outdoor heat exchanger disposed outside a vehicle compartment, an expansion valve, and an indoor heat exchanger disposed inside the vehicle compartment are connected together in this order through refrigerant pipes.
For example, a vehicle air conditioner of Patent Document 1 includes, as indoor heat exchangers, an upstream indoor heat exchanger disposed upstream in an air flow direction, and a downstream indoor heat exchanger disposed downstream in the air flow direction. The downstream indoor heat exchanger serves as a radiator in both of an air-heating operation mode and an air-cooling operation mode. Moreover, the upstream indoor heat exchanger serves as a heat absorber in both of the air-heating operation mode and the air-cooling operation mode.
Strong air-heating is required for the air-heating operation mode particularly under low outdoor air temperature. However, there is a possibility that an air-heating capacity becomes insufficient when the upstream indoor heat exchanger serves as the heat absorber in the air-heating operation mode as described in Patent Document 1.
In view of the foregoing, the upstream indoor heat exchanger may also serve as the radiator in the air-heating operation mode as described in, e.g., Patent Document 2. That is, the refrigerant pipes are connected together such that refrigerant discharged from the compressor flows through the upstream indoor heat exchanger after flowing through the downstream indoor heat exchanger. This allows air heated by the upstream indoor heat exchanger to be re-heated in the downstream indoor heat exchanger, and therefore there is an advantage that the air-heating capacity can be improved. On the other hand, since depressurized refrigerant is, in the air-cooling operation mode, supplied to the upstream indoor heat exchanger to cause the upstream indoor heat exchanger to serve as the heat absorber, air-cooling can be also performed.